EvtHypWK.cc

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//--------------------------------------------------------------------------
//
// Environment:
//      This software is part of models developed at BES collaboration
//      based on the EvtGen framework.  If you use all or part
//      of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/BesCopyright
//      Copyright (A) 2006      Ping Rong-Gang, Pang Cai-Ying@IHEP
//
// Module: EvtHypWK.hh
//
// Description: To generate octet hyperon weak decays.
//
// Modification history:
//
//    Pang C.-Y., Ping R.-G.    Mar, 2007       Module created
//    Ping R.G. Apr. 2007  change to helicity amplitude method
//------------------------------------------------------------------------
//
#include "EvtHypWK.hh"
#include "../EvtGenBase/EvtDiracSpinor.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtHelSys.hh"
#include "../EvtGenBase/EvtId.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtReport.hh"
#include "../EvtGenBase/EvtVector4C.hh"
#include "../EvtGenBase/EvtdFunction.hh"
#include <iostream>
#include <stdlib.h>
#include <string>
 
using std::cout;
using std::endl;
 
EvtHypWK::~EvtHypWK() {}
 
void EvtHypWK::getName( std::string& model_name ) { model_name = "HypWK"; }
 
EvtDecayBase* EvtHypWK::clone() { return new EvtHypWK; }
 
void EvtHypWK::init() {
 
  // check that there are 0 arguments
  // checkNArg(0);
  checkNDaug( 2 );
 
  //  checkSpinParent(EvtSpinType::VECTOR);
  checkSpinParent( EvtSpinType::DIRAC );
 
  checkSpinDaughter( 0, EvtSpinType::DIRAC );
  checkSpinDaughter( 1, EvtSpinType::SCALAR );
  //  checkSpinDaughter(1,EvtSpinType::DIRAC);
}
 
void EvtHypWK::decay( EvtParticle* p ) {
 
  static EvtId PIP = EvtPDL::getId( "pi+" );
  static EvtId PIM = EvtPDL::getId( "pi-" );
  static EvtId PI0 = EvtPDL::getId( "pi0" );
  static EvtId PP  = EvtPDL::getId( "p+" );
  static EvtId PM  = EvtPDL::getId( "anti-p-" );
  static EvtId NP  = EvtPDL::getId( "n0" );
  static EvtId NM  = EvtPDL::getId( "anti-n0" );
 
  static EvtId LP  = EvtPDL::getId( "Lambda0" );
  static EvtId LM  = EvtPDL::getId( "anti-Lambda0" );
  static EvtId SPP = EvtPDL::getId( "Sigma+" );
  static EvtId SPM = EvtPDL::getId( "anti-Sigma-" );
  static EvtId SMP = EvtPDL::getId( "Sigma-" );
  static EvtId SMM = EvtPDL::getId( "anti-Sigma+" );
 
  static EvtId XP  = EvtPDL::getId( "Xi-" );
  static EvtId XM  = EvtPDL::getId( "anti-Xi+" );
  static EvtId X0P = EvtPDL::getId( "Xi0" );
  static EvtId X0M = EvtPDL::getId( "anti-Xi0" );
 
  static int count = 0;
 
  //  if(count==0) findMaxPro(p); //using the default getProbMax() in
  //  EvtGenBase/EvtDecayProb.cc
  count += 1;
 
  p->initializePhaseSpace( getNDaug(), getDaugs() );
 
  EvtParticle *l1, *l2;
  l1               = p->getDaug( 0 );
  l2               = p->getDaug( 1 );
  EvtVector4R DRP4 = l1->getP4();   // Dirac Daughter
  EvtVector4R MEP4 = l2->getP4();   // Meson Daughter
  EvtVector4R PRP4 = p->getP4();    // Parent Momentum
  EvtHelSys   angles( PRP4, DRP4 ); // using helicity sys.angles
  double      tht = angles.getHelAng( 1 );
  double      ph  = angles.getHelAng( 2 );
  double      gmm = 0;
 
  EvtVector4R pDaug = l1->getP4();
  double      p3    = pDaug.d3mag();
 
  double M  = p->mass();
  double M2 = M * M;
  double m  = l1->mass();
  double m2 = m * m;
  double theta, phi, alpha, beta, ga; // the following is the
 
  EvtId p1, d1, d2;
  p1 = p->getId();
  d1 = l1->getId();
  d2 = l2->getId();
 
  if ( p1 == XP )
  {
    alpha = -0.46;
    phi   = -2.1;
  }
  else if ( p1 == XM )
  {
    alpha = 0.46;
    phi   = -2.1;
  }
  else if ( p1 == X0P )
  {
    alpha = -0.41;
    phi   = 21.0;
  }
  else if ( p1 == X0M )
  {
    alpha = 0.41;
    phi   = 21.0;
  }
  else if ( p1 == LP )
  {
    alpha = 0.64;
    phi   = -6.5;
  }
  else if ( p1 == LM )
  {
    alpha = -0.64;
    phi   = -6.5;
  }
  else if ( p1 == SMP )
  {
    alpha = -0.07;
    phi   = 10.0;
  }
  else if ( p1 == SMM )
  {
    alpha = 0.07;
    phi   = 10.0;
  }
  else if ( p1 == SPP )
  {
    if ( d1 == PP )
    {
      alpha = -0.98;
      phi   = 36.0;
    }
    else if ( d1 == NP )
    {
      alpha = 0.07;
      phi   = 167.0;
    }
    else { cout << "The decay is not discussed." << endl; }
  }
  else if ( p1 == SPM )
  {
    if ( d1 == PM )
    {
      alpha = 0.98;
      phi   = 36.0;
    }
    else if ( d1 == NM )
    {
      alpha = -0.07;
      phi   = 167.0;
    }
    else { cout << "The decay is not discussed." << endl; }
  }
  else { cout << "The decay is not discussed."; }
  if ( getNArg() > 0 ) { alpha = getArg( 0 ); }
 
  double FP = sqrt( ( 1 + alpha ) / 2. );
  double FM = sqrt( ( 1 - alpha ) / 2. );
 
  vertex( 0, 0, Djmn( 0.5, 0.5, 0.5, ph, tht, gmm ) * FP );
  vertex( 0, 1, Djmn( 0.5, 0.5, -0.5, ph, tht, gmm ) * FM );
  vertex( 1, 0, Djmn( 0.5, -0.5, 0.5, ph, tht, gmm ) * FP );
  vertex( 1, 1, Djmn( 0.5, -0.5, -0.5, ph, tht, gmm ) * FM );
 
  return;
}